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Balun and magnetic resonance imaging apparatus

a technology of magnetic resonance imaging and balun, which is applied in the direction of one-port networks, instruments, and reradiation, can solve the problems of unbalanced current flowing in aground lines, equipment such as the rf coil, to which the coaxial cable is connected, and can become susceptible to various noise, so as to effectively block the common mode noise and improve the performance of the rf coil

Active Publication Date: 2011-11-03
FUJIFILM HEALTHCARE CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention relates to a technique for improving the performance of a magnetic resonance imaging (MRI) apparatus by blocking common mode noise. The MRI apparatus uses a coaxial cable to connect the RF coil to the test subject, and the RF coil and the receive RF coil are also connected via a coaxial cable. However, if there is a large amount of power or extremely high frequency, the coaxial cable may become unevenly balanced, causing common mode noise. This noise can affect the performance of the RF coil and the image quality of the MRI. To address this issue, a balun is used to create a parallel resonance circuit that can tune to the common mode noise and reduce its impact. The resonance frequency of the balun is determined by the formula (1). The technical effect of this invention is to enhance the performance of the MRI apparatus by blocking common mode noise and improving image quality.

Problems solved by technology

However, if a large amount of power or extremely high frequency is treated, there may be cases where coupling occurs between the coaxial cable and the test subject or the like.
In this state, noise referred to as “common mode noise” may occur simultaneously reducing the shielding effect of the coaxial cable, and thus the cable may become susceptible to various noise.
The common mode noise represents unbalanced current which flows in aground line.
In some cases, this noise may propagate through a floor or a ground surface, and come back after going along a large loop while picking up various types of noise.
Therefore, equipment such as the RF coil, to which the coaxial cable is connected, is subjected to this noise.
Furthermore, there may be an unexpected impact also on the coaxial cable itself, not only on the equipment being connected.
If this kind of noise occur within the MRI apparatus, the coaxial cable may further become susceptible to coupling (specifically, electromagnetic radiation or electromagnetic induction), due to a structural reason.
Consequently, performance of the RF coil to which the coaxial cable is connected may be degraded, and further deteriorating an image quality of the MRI.
In some cases, unbalance of the characteristic impedance which occurs within the coaxial cable may cause generation of reflected electric power.

Method used

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  • Balun and magnetic resonance imaging apparatus
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  • Balun and magnetic resonance imaging apparatus

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first embodiment

[0049]Hereinafter, a first embodiment to which the present invention is applied will be explained. In the following descriptions, elements having the same function are labeled the same in all the figures for explaining the embodiments of the present invention, and tedious explanations will not be made.

[0050]An explanation will be made as to the overall configuration of the MRI apparatus according to the present embodiment. FIG. 1 illustrates overviews of the MRI apparatus according to the first embodiment. In the figure, the z-axis direction of the coordinate 9 indicates a static magnetic field direction. The MRI apparatus 100 shown in FIG. 1A is provided with a magnet 101 of the horizontal magnetic field system. The MRI apparatus 200 shown in FIG. 1B is provided with a magnet 201 of the vertical magnetic field system. Each of the MRI apparatuses 100 and 200 is provided with a table 120 for placing a test subject 103 thereon. The present embodiment is applicable to any of the MRI ap...

second embodiment

[0122]Next, a second embodiment to which the present invention is applied will be explained. The MRI apparatus according to the present embodiment is basically the same as the first embodiment. In the present embodiment, the balun formation circuit in which two serial resonance circuits 310 and 320 are connected in parallel is inductively connected with the coaxial cable 10, magnetically by using magnetic coupling, instead of physically connecting therebetween directly. Hereinafter, an explanation will be made featuring a configuration that is different from the first embodiment.

[0123]FIG. 10A illustrates a shape of the balun 118-2 of the present embodiment. The balun formation circuit 300-2 of the present embodiment is provided with a first serial resonance circuit 310 and a second serial resonance circuit 320 being connected in parallel, and a conductor 350 which is connected in parallel with those circuits. As illustrated, unlike the first embodiment, the balun formation circuit ...

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Abstract

The present invention provides a technique for maintaining a function for effectively blocking common mode noise with a simple configuration, even in the case where unbalance occurs in characteristic impedance of a coaxial cable in an MRI apparatus, and improving the performance of an RF coil. In a circuit where a balun is established by parallel connection with the coaxial cable, multiple serial resonance circuits having different resonance frequencies are connected in parallel. A value of each constitutional element of each of the serial resonance circuits is adjusted in such a manner that the frequency for blocking the common mode noise of the entire balun falls into a range between the resonance frequencies of these serial resonance circuits.

Description

TECHNICAL FIELD[0001]The present invention relates to a technique for enhancing performance of a magnetic resonance imaging (MRI) apparatus, and more particularly, it relates to a technique for blocking common mode noise.BACKGROUND ART[0002]The MRI apparatus is a medical image diagnostic system which excites magnetic resonance in atomic nuclei within a section crossing a test subject, and obtains a tomographic image of the cross section according to nuclear magnetic resonance signals being generated. The MRI apparatus firstly conveys power generated from a radio frequency (RF) power source, to a transmit RF coil. Next, by using the transmit RF coil, the radio frequency is irradiated to the test subject so that a nuclear magnetic resonance signal of a hydrogen nucleus (1H) is generated. Next, the nuclear magnetic resonance signal thus generated is detected by a receive RF coil which is adhered to the test subject, and thereafter, a receiver acquires the signal. Finally, the signal be...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): G01R33/32H03H7/42
CPCG01R33/3685
Inventor OTAKE, YOSUKESOUTOME, YOSHIHISAKANEKO, YUKIOBITO, YOSHITAKAOCHI, HISAAKIHIRATA, KOJI
Owner FUJIFILM HEALTHCARE CORP